Thermal Rearrangement Kinetics in ∆2-Thujene
Data for (+)-(1S,4R,5R)-1-isopropyl-4-methylbicyclo[3.1.0]-
hex-2-ene [(+)-trans-2]: [R]19.5D +30.8 (neat); d224 0.822 (micro-
pycnometer); IR (cm-1) 3055, 3035, 1602, 1026; MS (70 eV) m/z
(rel intens) 136 (25, parent), 121 (58), 109 (19), 107 (19), 105 (14),
94 (9), 93 (100, base), 92 (17), 91 (42), 79 (29), 77 (35), 65 (9),
large effect on the relative distribution among the four products
could be ascribed to a tertiary effect.
Experimental Section
1
43 (45), 41 (30), 39 (20); H NMR δ 5.78 (dd, J ) 6.0, 1.8 Hz,
Preparation of (+)-cis-1 and (+)-trans-2. Preparation of
mixtures of R- and â-thujenes from (+)-isothujone and (-)-thujone
by pyrolysis at 140° C of the lithium salts of the corresponding
tosylhydrazones has already been described in detail.3b Fractions
from the initial isolation, rich in ∆2-thujenes, are redistilled in the
spinning band column to give almost pure (+)-cis-1 (bp760 ≈ 146.5
1H), 5.14 (d, J ) 6.0 Hz, 1H), 3.10 (quintet, J ) 6.6 Hz, 1H), 1.35
(quintet, J ) 6.6 Hz, 1H), 1.19 (m, 1H), 1.01 (d, J ) 6.6 Hz, 3H),
0.97(d, J ) 6.6 Hz, 3H), 0.93, (d, J ) 6.6 Hz, 3H), 0.44 (m, 1H),
0.20 (t, J ) 3.6 Hz, 1H); 13C NMR δ 134.7, 133.8, 42.6, 41.6,
31.0, 25.3, 21.0, 20.8, 17.2, 17.1.
°C), (+)-trans-2 (bp760 ≈ 149.5 °C), and pure ∆3-thujene (bp760
152.5 °C).
)
Data for (-)-(1S,5R,6R)-3-isopropyl-6-methylbicyclo[3.1.0]-
hex-2-ene [(-)-exo-3]: [R]20D -61.8 (c 0.86, CCl4) (when derived
from (+)-cis-1); IR (cm-1) 3066 (m), 3054 (s), 3030 (s), 1623 (m),
1469 (s), 1388 (m), 1379 (m) (identical to compound V of Doering
Ratios among (+)-cis-1, (+)-trans-2, and ∆3-thujene were
sensitive to conditions as explicated in Table S-1. These reactions
were effected in a 25 mL, two-necked, round-bottomed flask with
a magnetic stirrer. Immediately after the additions at 30-35 °C,
which took ∼30 s, solvent was removed in the vacuum of a water
aspirator, leaving a salt which was freeze-dried for ∼1 h. The flask
was then placed in an oil bath at 140 °C and pyrolyzed at ∼13
Torr. The thujenes were trapped at -75 °C and analyzed by GC
on column A at 70 °C. The results of the various modifications to
this procedure are given in Table S-1.
1
and Lambert3a); H NMR δ 5.55 (t, J ) 1.8 Hz, 1H), 2.48 (dd, J
) 16.8, 7.2 Hz, 1H), 2.22 (d, J ) 16.8 Hz, 1H), 2.14 (quintet, J )
7.2 Hz, 1H), 1.48 (quartet, J ) 3.0 Hz, 1H), 1.17 (sextet, J ) 3.0
Hz, 1H), 0.94 (m, 10 H), 0.26 (m, 1H); 13C NMR δ 149.1, 124.9,
36.4, 31.9, 29.6, 25.2, 23.8, 21.9, 21.8, 17.3.
Data for (+)-(1R,5S,6R)-3-isopropyl-6-methylbicyclo[3.1.0]-
hex-2-ene [(+)-endo-4]: [R]21D +147 (c 0.37, CCl4) (when derived
from (+)-cis-1); IR (cm-1) 3053 (m), 3035 (s), 3019 (m), 1630
(m), 1460, 1461 (s), 1380 (s), 1366 (s), 848 (vs), 829 (m, sh), 780
The final procedure employed follows. A solution of 6.48 g of
tosylhydrazone in 30 mL of anhydrous THF was treated with 14.5
mL of 1.6 N n-butyllithium in hexane (1.1 molar equivalents) at rt
under argon. After the now red solution had been stirred for 2 h,
an additional 14.5 mL of 1.6 N n-butyllithium was added dropwise.
After being stirred for a further 10 min, the solution was treated
with 3 mL of water and extracted with two 15 mL portions of
pentane. Concentration and distillation at ∼140 °C yielded 1.96 g
(72%) of a mixture of cis- and trans-∆2-thujene and ∆3-thujene in
1
(vs), 734 (s); MS m/z 136 (parent), 93 (base); H NMR δ 5.27 (s,
1H), 2.37 (dd, J ) 16.8, 8.4 Hz, 1H), 2.19 (quintet, J ) 7.2 Hz,
1H), 1.98 (d, J ) 16.8 Hz, 1H), 1.87 (m, 1H), 1.43 (m, 1H), 0.97
(t, J ) 7.2 Hz, 6H), 0.85 (s, 4H); 13C NMR δ 152.2, 120.2, 32.0,
29.9, 28.3, 22.3, 22.1, 19.7, 16.1, 6.4.
Data for trans-3-isopropyl-5-vinylcyclopentene (5): [R]20
D
+191 (c 0.20, CCl4) (when derived from (+)-cis-1); IR (cm-1) 3076
(s), 3054 (s), 1815 (m), 1633 (s), 1608 (m), 1463 (s), 1370, 1359
(m) (identical to compound VI of Doering and Lambert3a); MS
1
the ratio 100:47:9 (by H NMR).
1
Thermal Reaction of ∆2-Thujenes. Samples of pure (+)-cis-1
and (+)-trans-2 were sealed in separate ampules of Pyrex glass
and heated simultaneously at ∼237 °C in a tubular furnace. On
analysis by GC (column A), each reaction mixture showed the same
five peaks, their intensities differing depending on the starting
thujene. Pure samples of cis-1, trans-2, 5, exo-3, and endo-4 were
collected by preparative GC employing a 6 m column of 26.8%
PCEP (1,2,3-tris(2-cyanoethoxy)propane on 60/80 mesh Chro-
mosorb P) at 80 °C with He as a carrier gas flowing at 60 mL of
He/min. Retention times at 50 mL of He/min for cis-1, trans-2, 5,
exo-3, and endo-4 are 5.62 (relative retention time 1.00), 6.00 (1.07),
7.22 (1.28), 8.81 (1.57), and 10.48 (1.86) min, respectively. Specific
rotations, NMR spectra, IR spectra, and mass spectra follow.
Data for (+)-(1S,4S,5R)-1-isopropyl-4-methylbicyclo[3.1.0]-
hex-2-ene [(+)-cis-1]: [R]25 +85.6 (absolute EtOH); [R]24
m/z 136 (parent), 93 (base); H NMR δ 5.75 (m, 1H), 5.68 (m,
1H), 5.64 (m, 1H), 5.01 (dq, J ) 17.3, 1.2 Hz, 1H), 4.91 (dq, J )
9.6, 1.2 Hz, 1H), 3.24 (m, 1H), 2.45 (m, 1H), 1.70 (m, 2H), 1.41
(sextet, J ) 6.6 Hz, 1H), 0.84 (d, J ) 6.6 Hz, 3H), 0.80 (d, J )
6.6 Hz, 3H); 13C NMR δ 142.8, 134.7, 134.0, 113.0, 52.5, 49.9,
34.9, 32.9, 20.7, 20.6.
Acknowledgment is made to the donors of the Petroleum
Research Fund, administered by the American Chemical Society,
for early support of this research, while our gratitude is
expressed to the Norman Fund in Organic Chemistry in memory
of Ruth Alice Norman Weil Halsband and Edward A. Norman
for more recent support. We are grateful to Harvard University
for its generosity in providing laboratory facilities to E.K.G.S.
during the period 1967-1968.
D
546
+101.4 (c 5.8, CHCl3); MS (70 eV) m/z (rel intens) 136 (25, parent),
121 (57), 109 (10), 107 (15), 105 (12), 94 (10), 93 (100, base), 92
(15), 91 (33), 79 (31), 77 (34), 65 (7), 43 (37), 41 (23), 39 (17); 1H
NMR δ 5.82 (dd, J ) 5.4, 1.8 Hz, 1H), 5.32 (d, J ) 5.4 Hz, 1H),
2.43 (q, J ) 7.2 Hz, 1H), 1.30 (quintet, J ) 7.2 Hz, 1H), 1.01 (d,
J ) 7.2 Hz, 3H), 0.98 (d, J ) 7.2 Hz, 4H), 0.89 (d, J ) 7.2 Hz,
Supporting Information Available: Table S-1 showing the
dependence of the products on the preparation conditions of
thujenes, Tables S-2 and S-3 summarizing untreated data from the
kinetic studies, and Table S-4 giving alternative calculations of
kinetic data at 237 °C. This material is available free of charge via
3H), 0.71 (dd, J ) 8.4, 3.6 Hz, 1H), 0.12 (t, J ) 3.6 Hz, 1H); 13
C
NMR δ 133.9, 133.4, 43.1, 41.7, 31.0, 28.2, 22.6, 22.3, 21.1, 21.0.
JO0609430
J. Org. Chem, Vol. 71, No. 15, 2006 5693